Applicants disclosed in U.S. patent application publication (2002/0132673 A1) a power transmission system. The system includes a damper for absorbing torque fluctuation and a torque limiter that interrupts torque transmission by breaking transmission passage when transmission torque exceeds a given torque.
However, examination of a prototype of the above system exhibits a problem. Namely, of the system the power transmission, i.e., a pulley 1, is equipped with a cover 9 as shown in FIGS. 8A, 8B. The cover 9 is hooked to be fixed with the pulley 1 for inhibiting the damper 5 from departing due to its deformation. When transmission torque exceeds a given torque and the torque limiter 8 is thereby broken, the cover 9 slips out from the pulley 1 and a fragment of the broken torque limiter 8 or the damper 5 is outwardly dispersed. After investigating the causes of the preceding, the following are found.
As the torque limiter 8 is broken, a driving-unit-side portion 8A of the torque limiter 8 continues to be rotated while the other driven-unit-side portion 8B stops. Both the portions 8A, 8B thereby collide with each other, and the driving-unit-side portion 8A mounts on the driven-unit-side portion 8B to be outwardly displaced in the rotation axial direction, as shown in FIG. 9. Pushing force due to the displacement causes the cover 9 to slip out from the pulley 1.
To deal with the problem, it is likely that a clearance is previously provided between the cover and pulley as meeting the maximum displacement, i.e., equivalent to thickness of the torque limiter. However, providing excessive clearance lessens effectiveness in an original function that restricts deformation of the damper. Furthermore, providing the additional clearance results in reducing clearance with other devices. This may generate interference between the cover and other devices.